The 1G-GTE is a JDM-only engine which first appeared in the Soarer but was also used in practically all RWD six cylinder Toyotas at one time or another, including the GA70 Supra, Chaser, MkII, Cresta, etc.
It's a smallish 2 litre inline six featuring a DOHC 24 valve cylinder head, EFI, twin CT12 turbos, and an intercooler. There were several versions of the 1G-GTE but the most powerful version was rated at 210hp. More specs can be found here
This engine existed only because of Japan's strange vehicle registration laws, which basically means it's much cheaper to own a 2 litre turbo car than a 3 litre NA car. That's why practically all manufacturers offer their larger cars with small turbocharged engines (eg Nissan has the RB20DET). These engines don't make sense outside of Japan which is why they're not exported.
As for swaps, they're popular here in Australia for smaller cars (usually Celicas) but I know of only one guy who's putting one in a MkII Supra. He occasionally posts here under the name JustCallMeFrank. He's putting a 1G-GTE in a JDM Celica XX which came with a G series engine from the factory, so the swap will be relatively easy for him. If you didn't have a GA60 Celica XX to start with I don't think this swap would be worth the trouble.